Conductivity-depth conversion method for aviation transient electromagnetic data

Abstract

The invention discloses a conductivity-depth conversion method for aviation transient electromagnetic data. The algorithm is divided into three steps of calculating apparent conductivity, calculating apparent depth and estimating imaging depth. Firstly, a function equation which relates one-to-one mapping of conversion between all uniform half-space model conductivity and response data is proposed and thus a data function table for query of transient apparent conductivity values is established on the basis so that a non-uniqueness problem generated when the transient apparent conductivity is inquired directly through an induced electromotive force and a no-solution problem of the transient apparent conductivity are prevented and a reliable apparent resistivity value is obtained. Secondly, 1.28 times of the maximum amplitude of an induced electric field in a uniform half space is used as the apparent depth, which is rapidly inquired and obtained through the pre-built data function table and an approximate calculation formula of imaging depth is proposed and the layer thickness of the model is defined based on the apparent-depth change during two adjacent time-delay periods so that a conductivity-depth conversion result is obtained.

Description

technical field [0001] The invention provides a conductivity-depth conversion technology of aeronautical transient electromagnetic, which belongs to the data processing and interpretation method category of time-domain aeronautical electromagnetic data. Background technique [0002] The airborne electromagnetic survey method has the technical characteristics of large detection depth, high measurement accuracy, high survey efficiency, and low work cost. Applications. Due to the large volume and poor quality of airborne transient electromagnetic data and high requirements for processing speed, the conductivity-depth imaging (Conductivity-Depth Imaging, CDI) method can quickly process the observation data into a subsurface conductivity-depth profile, which can Fast delineation of target anomalies or as an initial model for inversion. Compared with the inversion method (Ellis, 1998; Christensen, 2009; Cox, 2010; Mao Lifeng, 2011), the CDI method has a fast calculation speed, do...

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Problems solved by technology

However, because the imaging depth estimation method is very difficult, Huang's imaging depth is provided in the form of an empirical relationship graph, and the algorithm for imaging depth is not provided. In addition, the parameters of the aeronautical transient electromagnetic system aimed at by the present invention are obtained from Huang's τ-α data The apparent conductivity of the table query is not unique. The τ-α curves corresponding to different conductivities in the high conductivity section are intersected, and the apparent conductivity value obtained when the model conductivity value is high is not reliable.

In the airborne transient electromagnetic method and the ground transient electromagnetic method, when the apparent conductivity value is directly calculated from the induced electromotive force data, the induced electromotive force is related to the uniform half-space model and the conductivity is a double-valued function. How to obtain the only reliable apparent conductivity Conductivity is very difficult, and there is no good solution. In addition, due to the complexity of the medium, the imaging depth cannot only use the apparent depth. For example, the apparent depth of the previous delay may be greater than the apparent depth of the next delay, and it is impossible to obtain a reasonable Imaging result

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